Light Fixture Troubleshooting

Troubleshooting a light fixture is a project that even less handy folks can do successfully.

The day when light fixtures were either incandescent or fluorescent is a thing of the past. Today the homeowner will also encounter LED -- light-emitting diode -- fixtures. Fortunately, the troubleshooting procedures are basically the same for all three types. The good news is that all you will need is a noncontact voltage tester and a digital multimeter. If you need to buy a digital multimeter, buy an auto-ranging meter instead of a manual-ranging meter.

The Continuity Test

The basic test used when troubleshooting any light fixture is the continuity test. A continuity test determines when an electrical circuit is good or bad, continuous or broken. The first test to be performed, before testing the fixture itself, is to determine whether or not there is voltage available at the lighting outlet box. A voltage check can be performed with either the AC voltage function on your digital multimeter or with the noncontact voltage tester. The noncontact voltage tester is recommended for the homeowner because it does not require you to actually touch the probe to live, current-carrying wires; all you have to do is bring it near the light fixture when the light switch is on.

Troubleshooting Incandescent Fixtures

Turn off the circuit breaker for that branch circuit at the service panel. Check the circuit again with the voltage tester to make sure that you have turned off the right circuit breaker. Lower the light fixture from the outlet box, and then check to see that there is a good connection between the fixture wires and the branch circuit wires. Those connections are made using plastic, screw-on wire nuts and can slip out of them if installed improperly. Disconnect the fixture wires if you find the connections were good. You have to disconnect the wires so you can check the continuity. With the meter set on the ohms function, check for continuity between the white fixture wire and the metal shell inside the light socket. If there is continuity, the meter will display “0.000” on its LCD. If the socket is bad, the LCD will display “O.L.” Check for continuity between the black fixture wire and the brass button in the lamp socket. The LCD will either display “0.000” or “O.L.” If the socket checks out OK but the light still does not work, the brass contact of the socket is not making contact with the base of the bulb and needs to be pried away from the base of the socket.

Checking Fluorescent Fixtures

When it comes to troubleshooting fluorescent lights, your senses of sight, hearing and will go a long way to helping you locate the problem. If there is voltage present but the light fails to come on, first check to see if the light bulbs are burned black at their ends. If they have blackened ends, replace the bulbs and your problem will most likely be solved. If the light flickers but does not come on, the problem again may just be bad bulbs. Usually the flickering will be combined with blackened ends. A buzzing sound and/or a hot, tarry smell is indicative of a bad ballast that requires replacement. Bad contact between the pins on the light bulbs and the brass strips in their sockets is not a common problem, but it can happen. With bad sockets, replace them; do not try to fix them.

Troubleshooting LED Lights

Troubleshooting LED lamps is the same as for incandescent lights unless they are LED rope lights. With rope lights, if there is voltage present and the circuit connections are good, the only thing you can do is replace them.

Bad Circuit Neutral

A broken neutral wire somewhere between the lighting outlet box and the neutral bar in the service panel will also keep the light from operating. The noncontact voltage tester will still indicate the presence of voltage even if the neutral is bad. To determine if you have a neutral problem, you will have to use your digital multimeter. Set the meter's function switch to AC volts, turn on the circuit breaker and touch the probes to the circuit wires. If the neutral is good, the meter will display “120” on its LCD; if the neutral is broken, it will display “0.000.” A broken neutral is rare, but it can happen. Locating a broken neutral wire inside the walls of your home requires special circuit-tracing equipment and is better left to professionals.

About the Author

Based in Colorado Springs, Colo., Jerry Walch has been writing articles for the DIY market since 1974. His work has appeared in “Family Handyman” magazine, “Popular Science,” "Popular Mechanics," “Handy” and other publications. Walch spent 40 years working in the electrical trades and holds an Associate of Applied Science in applied electrical engineering technology from Alvin Junior College.